Carcinogenesis, Vol 19, 663-666, Copyright © 1998 by Oxford University Press
S Mikkelsen, B Berne, B Staberg and A Vahlquist
Vitamin A and its derivatives (retinoids) exert modulatory effects on
epithelial differentiation and are used therapeutically against skin
cancers, but the role of dietary vitamin A in ultraviolet (UV)-induced
carcinogenesis is far from clear. To study this process, 220 hairless mice
were given diets containing low (0.3-0.6 mg/kg; A-) or high (4-6 mg/kg; A+)
amounts of retinol, which resulted after 2 months in an approximately
4-fold difference in liver and skin vitamin A levels as determined by HPLC.
Commencing after 1 month of diet, daily irradiations with UVB (280-320 nm)
or UVAB (280-380 nm) were given to 176 of the animals for 18 weeks
(cumulative doses of UVB and UVA: 26 J/cm2 and 168 J/cm2, respectively).
The first skin tumours, known to be squamous cell carcinomas, appeared
after 35 weeks in the UVAB- irradiated A+ animals and 5-6 weeks later in
the other groups. After one year the frequency of tumour-bearing animals
was 49-63% in the A+ groups and 28-39% in the A- groups (P = 0.003). Two
months later the corresponding figures were 66-72% and 50-53%, respectively
(P = 0.014). Disregarding the effect of dietary vitamin A, there was no
difference in the final tumour incidence between UVB- and UVAB-irradiated
animals. The epidermal vitamin A content at 72 h post-irradiation was
approximately 60% lower in A+ animals and approximately 10% lower in A-
animals compared with the non-irradiated controls. Rather than protecting
against skin cancer, a diet rich in vitamin A seems to facilitate UV
carcinogenesis in hairless mice. A possible explanation is that
photodecomposition of excessive vitamin A generates short-lived
intermediates that may act as photosensitizers during cutaneous
carcinogenesis.
ARTICLES
Potentiating effect of dietary vitamin A on photocarcinogenesis in hairless mice
Department of Dermatology, The Finsen Institute, Copenhagen, Denmark.
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